We have a large concrete water fountain, sitting in shallow pond lined with a fibre glass liner.. the fountain is constantly getting black and mucky and algae etc. we generally cleaned it with a water blaster...we realise this has damaged the surface of the fountain....we can’t fix this now..but we want to seal it with something to stop it eroding away any more and to make it easier to clean and hopefully prevent algae and mould , black muck etc for coming on the fountain. After some tips and advise on what to use to seal the fountain and the pond liner and then regular clean ways to help keep it looking sparkling clean all the time. We had tried all sorts of pond blocks things from Bunnings..but made no difference...urgently need some suggestions first on what to use to pain the/seal the fountain with...thanks